RPR is a packet service oriented transmission technique, which effectively combines distinctive service features of telecommunications with data service oriented high efficiency bandwidth allocation, flexibility and expandability of Ethernet, and provides an optimized bandwidth management and a multi-priority packet transmission scheme with a high performance to cost ratio for operators.
FIG. 1 is a schematic diagram illustrating the structure of an RPR network and the structure of one station on the RPR in the prior art. As shown in FIG. 1, an RPR network is of double-ringlet structure with the ringlets rotating in the mutually inverse directions, comprising an inner ringlet (ringlet 1) and an outer ringlet (ringlet 0). The RPR network can support 255 stations interconnected, as S0˜S254 shown in FIG. 1. Both the inner ringlet and the outer ringlet of the RPR can transmit and receive data frames. Each of the stations on the RPR includes a Medium Access Control (MAC) client, a physical layer entity and an MAC entity. The MAC entity further includes one MAC control entity, one inner data path entity associated with the inner ringlet and one outer data path entity associated with the outer ringlet. The physical layer entity further includes a west physical layer entity and an east physical layer entity. The outer ringlet receives data from the west physical layer entity and transmits data via the east physical layer entity, while the inner ringlet receives data from the east physical layer entity and transmits data via the west physical layer entity, thus the MAC client can receive and transmit data via either the inner ringlet or the outer ringlet.
For the RPR network, one of the key techniques to be realized is to provide different service classes for client entities and ensuring the quality of service (QoS) required by the protocol. According to the RPR protocol, the RPR MAC entity should provide three classes of data service: class A, class B, and class C, each of which has the following characteristics:
Class A service is a service with both an ensured bandwidth and an ensured jitter performance. Class A service in the RPR MAC entity can be further divided into class A0 service and class A1 service, wherein, the bandwidth of the class A0 service is reserved, and the bandwidth can not be occupied by services with other classes or services of other stations. This class of service is mostly used to carry real time services with strict requirements for bandwidth and jitter. The characteristic of class A1 service is that the bandwidth and jitter are both ensured while the bandwidth is not reserved. That is, if there is no data of class A1 service to be transmitted, the bandwidth of class A1 service can be reclaimed by services with other classes or/and services of other stations so that the usage rate of bandwidth is increased. However, the accessing delay of class A1 service is longer than that of class A0 service.
Class B service in the RPR MAC entity can be further divided into class B0 service and class B1 service, wherein, the bandwidth of class B0 service is ensured, and the delay and jitter of class B0 service is ensured to a limited degree. Class B0 service is also referred to as class B-CIR service within a promised accessing rate. If there is no data of class B0 service to be transmitted, the bandwidth of class B0 service can be reclaimed by services with lower classes. Class B1 service is a class B service with the rate thereof exceeding the promised rate, which is a best effort service. Class B1 service is also referred to as a class B-EIR service, none of whose bandwidth, jitter or delay is ensured.
Class C service is a best effort service, none of whose bandwidth, jitter or delay is ensured.
In order to ensure the transmission bandwidth of services with different classes transferred in the RPR network, the RPR network needs to implement rate limitation to services uploaded to the ringlets with different service classes, and this rate limitation is a necessary precondition to realize all the different service classes sharing the network resources based on the pre-assigned bandwidth. A specific method of rate limitation includes: precisely obtaining the physical layer link bandwidth; and allocating the physical layer bandwidth to different stations and corresponding classes according to pre-configured rules so as to ensure the total bandwidth configuration of all the services whose bandwidths need to be ensured is no larger than the physical layer link bandwidth, so that the corresponding bandwidths of different services can be ensured. Under the circumstances that all the bandwidths of different services are ensured, the requirements in terms of jitter and delay can be automatically ensured by the adjusting mechanism of the RPR MAC entity.
However, since RPR is a data link layer technique, the PRP protocol requires that the RPR be carried on different physical layer entities. At present, there are several physical layer techniques, such as Synchronous Digital Hierarchy (SDH)/Synchronous Optical Network (Sonet) and Gigabit Ethernet/10 Gigabit Ethernet (GE/10GE) to be chosen. The data transmission can be successfully realized by a special encapsulation of the RPR packet or by adding certain overheads to the RPR packet before transmitting data via the physical layer techniques described above. For example, in terms of the SDH technique, firstly a certain length of overhead will be encapsulated to the packet (a RPR packet for example) to be sent, then the packet will be mapped to a transmission time slot of SDH/Sonet. In terms of the GE/10GE technique, a Preamble and a Start Frame Delimiter (SFD) will be added to the packet to be sent before transmitting the packet. Due to the added physical layer overhead in the process of encapsulation, the actual bandwidth assigned to the RPR MAC entity is narrower than the promised bandwidth. The loss of the bandwidth will probably lead to the problem that services with lower service classes forwarded by a station occupy the bandwidth of services with higher service classes uploaded to the ringlet from this station when link congestion occurs. For example, in an application, a class B_CIR service forwarded by a station may probably occupy the bandwidth of a class A0 service uploaded to the ringlet from this station, or a class C service forwarded by a station may probably occupy the bandwidth of a class A0 service uploaded to the ringlet from this station, so that expected service classes can not be truly ensured.